Bicycle propulsion system for electric bicycle conversion

ABSTRACT

A bicycle propulsion system including a concentric rotor assembly and a chassis assembly. The concentric rotor assembly: defines an outer drive surface; defines an inner retention surface; includes a set of sprocket brackets arranged about the inner retention surface of the concentric rotor assembly and configured to engage with teeth of a bicycle sprocket; and is configured to engage around the bicycle sprocket, wherein a center axis of the outer drive surface is concentric with a rotational axis of the bicycle sprocket. The chassis assembly: is configured to secure to a stay of the bicycle; includes a retention subassembly configured to translationally constrain the concentric rotor assembly relative to the chassis assembly; includes a drive subassembly configured to engage the outer drive surface of the concentric rotor assembly; and includes a motor configured to rotate the concentric rotor assembly via the drive subassembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation application of U.S. patentapplication Ser. No. 16/793,588, filed on 18 Feb. 2020, which claims thebenefit of U.S. Provisional Application No. 62/806,817, filed on 17 Feb.2019, and U.S. Provisional Application No. 62/806,898, filed on 17 Feb.2019, each of which is incorporated in its entirety by this reference.

TECHNICAL FIELD

This invention relates generally to the field of electric bicyclepropulsion and more specifically to a new and useful electric bicycleconversion system in the field of electric bicycle propulsion

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a system;

FIG. 2 is a schematic representation of the system;

FIG. 3 is a schematic representation of the system;

FIG. 4 is a schematic representation of the system;

FIG. 5 is a schematic representation of the system;

FIG. 6 is a schematic representation of the system;

FIG. 7 is a schematic representation of the system;

FIG. 8 is a schematic representation of the system;

FIG. 9 is a schematic representation of the system;

FIG. 10 is a schematic representation of the system;

FIG. 11 is a schematic representation of the system;

FIG. 12A is a schematic representation of the system;

FIG. 12B is a schematic representation of the system; and

FIG. 13 is a schematic representation of the system.

DESCRIPTION OF THE EMBODIMENTS

The following description of embodiments of the invention is notintended to limit the invention to these embodiments but rather toenable a person skilled in the art to make and use this invention.Variations, configurations, implementations, example implementations,and examples described herein are optional and are not exclusive to thevariations, configurations, implementations, example implementations,and examples they describe. The invention described herein can includeany and all permutations of these variations, configurations,implementations, example implementations, and examples.

1. Bicycle Propulsion System

As shown in FIGS. 3 and 6 , a bicycle propulsion system 100 includes: aconcentric rotor assembly 102; and a chassis assembly 104. Theconcentric rotor assembly 102: comprises a first rotor element 134attached to a first sprocket bracket 151 configured to engage with afirst bicycle sprocket; comprises a second rotor element 136 attached toa second sprocket bracket 152 configured to engage the first bicyclesprocket; and is configured to define a circular outer drive surface132, to define a circular inner retention surface 133, and totransiently engage around the first bicycle sprocket in an engagedconfiguration of the concentric rotor assembly 102 via the firstsprocket bracket 151 and the second sprocket bracket 152. The chassisassembly 104: is configured to transiently secure to a bicycle frameelement; includes a retention subassembly configured to translationallyconstrain the concentric rotor assembly 102 relative to the chassisassembly 104 while the concentric rotor assembly 102 is engaged aroundthe first bicycle sprocket and the chassis assembly 104 is secured tothe bicycle frame element; includes a drive subassembly configured toengage the concentric rotor assembly 102 via the circular outer drivesurface 132; and comprises a motor 162 configured to rotate theconcentric rotor assembly 102 about a center axis of the circular outerdrive surface 132 via the drive subassembly, the motor 162 causingrotation of the first bicycle sprocket while the concentric rotorassembly 102 is engaged around the first bicycle sprocket.

One variation of the bicycle propulsion system 100, shown in FIGS. 3, 6,and 7 , includes: a concentric rotor assembly 102 and a chassis assembly104. In this variation, the concentric rotor assembly 102 is configuredto rigidly and transiently engage around a sprocket of a bicycle andincludes a set of sprocket brackets 150 arranged about the concentricrotor assembly 102, the set of sprocket brackets 150 configured toengage with teeth of the sprocket of the bicycle. In this variation, thechassis assembly 104: is configured to transiently secure to a frameelement of the bicycle; comprises a retention subassembly configured totranslationally constrain the concentric rotor assembly 102 relative tothe chassis assembly 104; includes a drive subassembly configured toengage the concentric rotor assembly 102; includes a motor 162configured to rotate the concentric rotor assembly 102 about a centeraxis of the concentric rotor assembly 102 via the drive subassembly;includes a sensor arm 171 configured to engage with a chain of thebicycle via a chain roller 176 biased against the chain of the bicycle;and includes an electronics subsystem 180. In this variation, thiselectronics subsystem 180 is configured to: detect deflection of thesensor arm 171 caused by tension in the chain of the bicycle; andactivate the motor 162 to rotate the concentric rotor 130 based on thedeflection of the sensor arm 171.

One variation of the bicycle propulsion system 100, shown in FIG. 3 ,includes a concentric rotor assembly 102 and a chassis assembly 104. Inthis variation, the concentric rotor assembly 102: defines a circularouter drive surface 132; defines an inner retention surface 133;comprises a set of sprocket brackets 150 arranged about the innerretention surface 133 of the concentric rotor assembly 102 andconfigured to engage with teeth of a bicycle sprocket; and is configuredto transiently engage around the bicycle sprocket, wherein a center axisof the circular outer drive surface 132 is concentric with a rotationalaxis of the bicycle sprocket. In this variation, the chassis assembly104: is configured to transiently secure to a stay of the bicycle;includes a retention subassembly configured to translationally constrainthe concentric rotor assembly 102 relative to the chassis assembly 104;and includes a drive subassembly configured to engage the circular outerdrive surface 132 of the concentric rotor assembly 102; and includes amotor 162 configured to rotate the concentric rotor assembly 102 about acenter axis of the circular outer drive surface 132 via the drivesubassembly.

2. Applications

Generally, as shown in FIG. 1 , a bicycle propulsion system 100includes: a rotor configured to transiently mount to a sprocket of abicycle (e.g., a rear sprocket of the bicycle, front chainring of thebicycle); a chassis assembly configured to transiently mount to a frameelement of the bicycle (e.g., a chain stay of the bicycle, a seat stayof the bicycle); and a motor arranged in the chassis assembly andconfigured to drive the rotor, thereby generating additional torqueabout the sprocket of the bicycle and assisting a rider operating thebicycle.

More specifically, as shown in FIGS. 3, 4, 5, 6 and 7 , the bicyclepropulsion system 100 includes: a concentric rotor assembly 102including a set of sprocket brackets 150 configured to transientlyengage the sprocket of a bicycle in an engaged configuration andconfigured to release from the sprocket in a disengaged configuration;and a chassis assembly 104 that secures to the concentric rotor assembly102 in the engaged configuration, transiently mates to a chain stay orseat stay of the bicycle, and includes a motor 162 and drive subassemblythat transmits torque to the concentric rotor assembly 102. Theconcentric rotor assembly 102 is configured to open (or “split”) toenable installation over and removal from a sprocket of a rear cogset ofthe bicycle without necessitating removal of the rear wheel from reardropouts of the bicycle frame. The concentric rotor assembly 102 is alsoconfigured to close and latch around the sprocket in an engagedconfiguration in which the outer surface of the concentric rotorassembly 102 forms a continuous, circular outer drive surface 132; andin which sprocket brackets 150, extending toward the radial center ofthe concentric rotor assembly 102, engage teeth of the sprocket in orderto transmit torque between the outer drive surface 132 and the sprocket.The chassis assembly 104: includes a set of rollers configured to engageand retain the concentric rotor assembly 102 in a “hub-less wheel”configuration when the concentric rotor assembly 102 is installed on asprocket; includes an electronic motor; and includes a toothed drivebelt 164 that runs between these rollers and the outer drive surface 132of the concentric rotor assembly 102 and transmits torque from theelectric motor into the concentric rotor assembly 102, which thentransmits torque into the sprocket via the sprocket brackets 150.Furthermore, the chassis assembly 104 includes a boss or rest configuredto engage a seat stay or chain stay near rear drops of the bicycle frameand thus prevent rotation of the chassis assembly 104 about a pitch axisof the bicycle when the motor is actuated; and a strap or other couplerconfigured to wrap around the seat stay or chain stay of the bicycle andthus constrain rotation of the chassis assembly 104 about a yaw axis ofthe bicycle while the concentric rotor assembly 102 and the rollerscooperate to constrain translation of the chassis assembly 104 androtation of the chassis assembly 104 about a roll axis of the bicycle.

Thus, the chassis assembly 104 can be installed on a bicycle frame bywrapping the strap around a right seat stay or right chain stay of thebicycle near a rear dropout of the bicycle without additional tools. Theconcentric rotor assembly 102 can then be opened, a first sprocketbracket 151 that is coupled to a first rotor element 134 at a proximalend of the first sprocket bracket can be located on the innermostsprocket or the rear cogset of the bicycle. The first rotor element 134can then be fed into the chassis assembly 104 and along the retainingrollers. The second sprocket bracket 152, attached to a second rotorelement 136, can be closed against an opposite side of the sprocket andlatched to the first rotor element 134 and, by extension, the firstsprocket bracket 151 coupled thereto. The concentric rotor assembly 102and the chassis assembly 104 can thus cooperate: to fully constrain thechassis assembly 104 on the bicycle frame; and to enable the concentricrotor assembly 102 to rotate with the rear wheel of the bicycle bypassing along the rollers through the chassis assembly 104. A chainroller 176—coupled to a sensor subassembly 170—can then be folded toengage and ride along the bicycle's chain, a battery assembly 106 can beset in a bolder holder mounted on the bicycle frame, and a power cablecan be routed from the battery assembly 106 to the chassis assembly 104to complete assembly of the bicycle propulsion system 100 on thebicycle, such as in under one minute. Later, these elements of thebicycle propulsion system 100 can be similarly removed from the bicycleover a similar duration of time in order to return the bicycle to anunassisted configuration.

Therefore, the bicycle propulsion system 100 includes a chassis assembly104 and a concentric rotor assembly 102 that cooperate: to enable rapidinstallation onto a bicycle when a user desires pedal assistance (e.g.,in preparation for a commute); and to enable rapid removal from thisbicycle, such as when the user parks the bicycle in a public space orwhen the user no longer desires pedal assistance (e.g., in preparationfor a bike ride with friends or when cycling in a park), all withoutadditional tools and without necessitating removal of a wheel or othernative component from the bicycle.

Furthermore, as shown in FIGS. 12A and 12B the bicycle propulsion system100 can: monitor tension in the chain of the bicycle—which is related toapplication of torque to pedals of the bicycle by a user—via the chainroller 176 that rides on the chain and the sensor subassembly 170coupled to the chain roller 176; interpret a target output torque oroutput power of the motor directly from this chain tension; and modulatethe torque or power output of the motor accordingly. Because the sensorsubassembly 170 and the chain roller 176 are integrated into the chassisassembly 104, the bicycle propulsion system 100 can monitor this controlsignal (i.e., chain tension) and implement closed-loop controls tomodulate output torque or output power of the motor withoutnecessitating installation of an additional sensor or module on thebicycle.

Thus, the bicycle propulsion system 100 can be quickly installed onbicycles—of a wide range of geometries and sizes—by locating threesubsystems (i.e., the concentric rotor assembly 102, the chassisassembly 104, and the battery assembly 106) on the bicycle without anyadditional tools. When in use, the bicycle propulsion system 100 cansupply additional power to the rear cogset (e.g., a bicycle cassette, afreehub) of the bicycle in order to assist a cyclist in propelling thebicycle forward as a function of power output by the cyclist. Similarly,the bicycle propulsion system 100 can be quickly removed from thebicycle, again without additional tools. Therefore, the bicyclepropulsion system 100 can enable convenient and temporary conversion ofa purely-manual bicycle to an electric bicycle with pedal assistance andvice versa, thereby enabling a cyclist to rapidly and seamlesslytransition a single bicycle between a purely-manual configuration (e.g.,for sport) and an electric bicycle configuration (e.g., for commuting).

2.1 System Overview

In one example, the bicycle propulsion system 100 transfers power to thecogset of a bicycle via a concentric rotor assembly 102 installed arounda sprocket of the bicycle (i.e. a bicycle sprocket in a cassette,freehub, or chainring). The bicycle propulsion system 100 can include aconcentric rotor assembly 102 configured to engage with a rear sprocketof a bicycle or, more specifically, an innermost sprocket in the cogsetof the bicycle. Thus, the bicycle propulsion system 100 occupies onesprocket in a derailleur-based transmission of a bicycle while in theengaged configuration. In an alternative implementation, the bicyclepropulsion system 100 includes a concentric rotor assembly 102configured to engage with a front chainring of a bicycle.

Therefore, in the engaged configuration, the concentric rotor assembly102 is configured to circumscribe a sprocket and inwardly extends a setof sprocket brackets 150 (e.g., two or more) configured to engage theteeth of the sprocket, as shown in FIG. 11 . The concentric rotorassembly 102, in the engaged configuration shown in FIG. 8 , alsodefines a circular outer drive surface 132 (with which the drivesubassembly can engage) and a circular inner retention surface 133 (withwhich the retention subassembly can engage), thereby enabling componentswithin the chassis assembly 104 to rotate the concentric rotor assembly102 about a central axis aligned with the rotational axis of thesprocket, where the concentric rotor assembly 102 acts as a wheel in ahub-less wheel system. Additionally, the concentric rotor assembly 102can include two hinged (shown in FIG. 9 ) or fully separable memberswhich, when engaged with each other, cause the set of sprocket brackets150 to align with the sprocket, thereby rotationally constraining thesprocket relative to the concentric rotor assembly 102, as shown in FIG.10 .

As shown in FIGS. 3, 4, 5, 6, and 7 , the bicycle propulsion system 100includes a chassis subsystem that secures the bicycle propulsion system100 to a frame element of a bicycle and prevents rotation of thenon-rotating components of the bicycle propulsion system 100 (such asthe motor, electronics subsystem 180, drive subassembly, and retentionsubassembly) about the sprocket's rotational axis upon application oftorque to the concentric rotor assembly 102. Therefore, the bicyclepropulsion system can efficiently power transfer to the sprocket whilepreventing damage to the bicycle or the bicycle propulsion system 100due to unintended movement of the bicycle propulsion system 100 relativeto the frame of the bicycle. In addition to constraining thenon-rotating components of the bicycles relative to the frame of thebicycle, the chassis assembly 104 houses the motor 162, the electronicssubsystem 180 that controls the motor 162, the drive subassembly thattransmits power from the motor 162 to the concentric rotor assembly 102,and the retention subassembly that prevents translational movement ofthe concentric rotor assembly 102 relative to the chassis assembly 104while enabling rotation of the concentric rotor assembly 102 as ahub-less wheel.

In one implementation, the bicycle propulsion system 100 is configuredto secure to a rear chain stay of a bicycle. In this implementation, thechassis assembly 104: includes an attachment element that secures thechassis assembly 104 to the right chain stay of the bicycle; and definesa form factor that houses the abovementioned subassemblies andcomponents between the right chain stay, the rear wheel, and the rearderailleur of the bicycle.

In another implementation, the bicycle propulsion system 100 includes achassis assembly 104 that further includes a sensor arm 171 extendingfrom the chassis assembly 104 to engage with a chain of the bicycle, asshown in FIG. 2 . The sensor arm 171 can include a chain roller 176 thatis pressed or biased against the chain (e.g., via a spring acting on thesensor arm 171). Therefore, as a cyclist applies torque to the pedals ofthe bicycle, the chain tension increases, presses on the chain roller176, and causes the sensor arm 171 to deflect relative to its initialposition. Thus, the bicycle propulsion system 100 can estimate the powerapplied by a cyclist to the pedals of the bicycle during operation andcan scale the power output of the motor 162 based on this estimation.

In one implementation, the bicycle propulsion system 100 can include aseparate battery assembly 106 connected to the chassis assembly 104 viaa power cable 182 and/or a throttle assembly 108 for modifying the levelof assistance output by the bicycle propulsion system 100. Additionally,the bicycle propulsion system 100 can interface with an applicationinstalled on a mobile computation device (e.g., a smartphone, tablet,bike computer) to enable the cyclist to modify settings of the bicyclepropulsion device.

2.2 Examples

In one example application of the bicycle propulsion system 100, acyclist may install the bicycle propulsion system 100 in order toconvert her standard road bicycle into an electric bicycle to facilitatecommuting or to traverse more difficult terrain. The cyclist can theneasily remove the bicycle propulsion system 100: to use the bicycle forexercise; to comply with legal restriction on electric bicycles in aparticular area; to prevent theft of the bicycle propulsion system 100while parking her bicycle; or for any other reason. Likewise, thecyclist can easily reinstall the bicycle propulsion system 100 whenevershe desires pedal assistance.

In another example application, a bikeshare operator can install aninstance of the bicycle propulsion system 100 on each bicycle in a fleetof bicycles in order to electrically assist users of this fleet ofbicycles and improving the utility of these bicycles to commuters in anoperational region. Upon mechanical failure of any bicycle propulsionsystem 100, the bikeshare operator can remove the bicycle propulsionsystem 100 from the affected bicycle and replace the bicycle propulsionunit with a functional bicycle propulsion system 100 while the originalbicycle propulsion system 100 installed on the affected undergoesrepairs. Therefore, by utilizing the bicycle propulsion system 100, asopposed to a pedal assistance system integrated with the bicycle, thebikeshare operator can minimize downtime in the fleet of electric pedalassist bicycles.

3. Concentric Rotor Assembly

Generally, the bicycle propulsion system 100 includes a concentric rotorassembly 102 that is clamped around or that otherwise engages a sprocketof a bicycle cogset, as shown in FIGS. 1, 8, 9, and 10 . Morespecifically, the bicycle propulsion system 100 includes a concentricrotor assembly 102 configured to transiently engage around a sprocket ofa bicycle and including a set of sprocket brackets 150 arranged aboutthe concentric rotor assembly 102, the set of sprocket brackets 150configured to engage with teeth of a sprocket of the bicycle.Additionally, the bicycle propulsion system 100 includes a concentricrotor assembly 102 that: includes a circular outer drive surface 132 anda circular inner retention surface 133, thereby defining surfaces forthe retention subassembly to translationally constrain the concentricrotor assembly 102 relative to the chassis assembly 104 and for thedrive subassembly to transfer power from the motor 162 to the concentricrotor assembly 102. Furthermore, as shown in FIG. 9 , the bicyclepropulsion system 100 can include a concentric rotor assembly 102 thatfurther includes: a first rotor element 134 attached to a first sprocketbracket 151 and a second rotor element 136 attached to a second sprocketbracket 152, where the concentric motor 162 assembly defines thecircular outer drive surface 132 and the circular inner retentionsurface 133 during engagement of the first rotor element 134 and thesecond rotor element 136 in an engaged configuration. Thus, the bicyclepropulsion system 100 includes a concentric rotor assembly 102 that caneasily be engaged and disengaged from a sprocket of a bicycles and canefficiently and securely transfer power to the sprocket of the bicyclesfrom the drive subassembly and motor 162 of the bicycle propulsiondevice.

In one implementation, as shown in FIG. 9 , the bicycle propulsionsystem 100 includes a concentric rotor assembly 102 that furtherincludes two approximately semicircular rotor elements attached at oneend by a hinge and defining male and female components of a latch 140 onthe first rotor element 134 and the second rotor element 136respectively. Upon engagement of the first rotor element 134 with thesecond rotor element 136, the first rotor element 134 and the secondrotor element 136 define the circular outer drive surface 132 and thecircular inner retention surface 133.

In another implementation, the bicycle propulsion system 100 includes aconcentric rotor assembly 102 that further includes two approximatesemicircular rotor elements that a configured to be fully separable viatwo latch 140 s. Therefore, a user can couple each end of the two rotorelements to the corresponding end of the opposite rotor element, therebydefining the circular outer drive surface 132 and the circular innerretention surface 133.

Additional components and implementations of these components aredescribed in further detail below.

3.1 Concentric Rotor

Generally, the bicycle propulsion system 100 includes a concentric rotor130 as a primary component of the concentric rotor assembly 102. Morespecifically, the bicycle propulsion system 100 can include a concentricrotor 130 including a centerless disk defining a circular outer drivesurface 132 and defining a circular inner retention surface 133, wherethe circular outer drive surface 132 defines a toothed (i.e. geared)surface and the circular inner retention surface 133 is characterized bya diameter greater than the bicycle sprocket with which the concentricrotor 130 is configured to engage. Additionally, the bicycle propulsionsystem 100 can include a concentric rotor 130 that defines a thicknesssuch that the concentric rotor 130 is laterally stable under load whenbeing driven by the drive subassembly and while engaged with a bicyclesprocket, such as a thickness between 0.5 centimeters and 1.5centimeters.

In one implementation, the concentric rotor 130 is manufactured as asingle piece of rigid material before being divided into two or moreseparate rotor elements. For example, the concentric rotor 130 can bemanufactured from a metal such as stainless steel or aluminum alloy(such as 6061 or 7075). For example, the concentric motor 162 can bemilled and/or lathed from a single piece of metal. Alternatively, theconcentric rotor 130 can be stamped from a single piece of metal.However, the concentric rotor 130 can be manufactured in any other way.

In another implementation shown in FIG. 8 , the concentric rotor 130 caninclude a set of slots in order to reduce the weight of the concentricrotor 130 while leaving sufficient material to maintain structuralstability of the concentric rotor 130 under load from the drivesubassembly.

3.2 Outer Drive Surface

Generally, the bicycle propulsion system 100 can include a concentricrotor 130 defining a geared outer drive surface 132, in order tointerface with the drive subassembly. In one implementation, the bicyclepropulsion system 100 can include a concentric rotor 130 configured tointerface (i.e. mesh) with a toothed drive belt 164 (i.e. timing belt)housed by the chassis assembly 104. In this implementation, the outerdrive surface 132 can define a set of curved teeth configured tointerface with a rubber timing belt. Thus, by interfacing with a timingbelt, the bicycle propulsion system 100 can reliably transfer power fromthe motor 162 to the concentric rotor 130 without lubrication orfrequency maintenance.

In one implementation, the bicycle propulsion system 100, via theretention subassembly, holds the concentric rotor assembly 102 relativeto the chassis assembly 104 with a pair of retaining rollers that ridealong the outer drive surface 132. However, in order to prevent damageto the retaining rollers due to impact with the toothed outer drivesurface 132, the bicycle propulsion system 100 can include a chamferededge at the base of the teeth of the outer drive surface 132 configuredto engage the retaining rollers of the retention subassembly.

3.3 Inner Retention Surface

Generally, the bicycle propulsion system 100 can include a concentricrotor 130 defining an inner retention surface 133 at along its interiorcircular edge in order for the retention subassembly of the chassisassembly 104 to translationally constrain the concentric rotor 130 whilefeeding the concentric rotor 130 through the chassis assembly 104 suchthat the concentric rotor 130 rotates about its center axis. Morespecifically, the bicycle propulsion system 100 can include a concentricrotor 130 that defines a smooth inner retention surface 133 configuredto engage with inner retaining rotors. Additionally, to preventprocession of the concentric rotor 130 during rotation, the concentricrotor 130 can define a circular inner retention surface 133 that isconcentric with the outer drive surface 132 and the rotational axis ofthe sprocket with which the concentric rotor assembly 102 is configuredto engage. In one implementation, the concentric rotor 130 defines aninner retention surface 133 that includes a chamfer corresponding to aninterior chamfer of the inner retaining rollers 122 in the retentionsubassembly.

3.4 Rotor Elements

Generally, as shown in FIGS. 6 and 7 , the bicycle propulsion assemblyincludes a concentric rotor 130 that further includes two (partially orcompletely) separable rotor elements, each rotor element defining an arcof the complete concentric rotor 130, in order to enable a cyclist toopen the concentric rotor 130 around the sprocket of the bicycle andclamp the concentric rotor 130 around this sprocket. More specifically,the concentric rotor assembly 102 includes: a first rotor element 134attached to a first sprocket bracket 151 configured to engage with abicycle sprocket; and a second rotor element 136 attached to a secondsprocket bracket 152 configured to engage the bicycle sprocket. In oneimplementation, the concentric rotor assembly 102 includes: a firstrotor element 134 attached to a first sprocket bracket 151 in a set ofsprocket brackets 150; and a second rotor element 136 attached to asecond sprocket bracket 152 in the set of sprocket brackets 150 andconfigured to transiently couple to the first rotor element 134 todefine the circular outer drive surface 132 and the inner retentionsurface 133. Thus, upon engagement of the first rotor element 134 withthe second rotor element 136 (e.g., via latches and/or a hinge), thefirst rotor element 134 and the second rotor element 136 combine todefine the circular outer drive surface 132 and the circular innerretention surface 133.

In one implementation, the bicycle propulsion system 100 can include aconcentric rotor 130 manufactured from a single piece of material priorto being cut into a first rotor element 134 and a second rotor element136, thereby ensuring a precise fit between the first rotor element 134and the second rotor element 136.

In another implementation, the bicycle propulsion system 100 can includea first rotor element 134 and a second rotor element 136 that areapproximately equal in size to ensure approximately equal load isapplied to each side of the sprocket of the bicycle via the firstsprocket bracket 151 and second sprocket bracket 152 during rotation ofthe concentric rotor assembly 102.

In yet another implementation, the bicycle propulsion system 100 caninclude additional rotor elements each attached to correspondingsprocket brackets 150 in order to more fully circumscribe the sprocketof the bicycle with sprocket brackets 150. In this implementation, theset of rotor elements can include multiple latches and/or hinges toenable a user to engage the concentric rotor 130 around the sprocket ofthe bicycle.

3.4.1. Rotor Hinge and Latch

Generally, as shown in FIG. 9 , the bicycle propulsion system 100 caninclude a set of rotor elements coupled by a rotor hinge 138 at one sideof each rotor element and transiently connected, in an engagedconfiguration, by a latch 140. More specifically, the bicycle propulsionsystem 100 can include a concentric rotor assembly 102 that furtherincludes: a hinge connecting a first rotor element 134 to a second rotorelement 136, the hinge defining a rotational axis parallel to the centeraxis of the circular outer drive surface 132; a latch 140 inset into thefirst rotor element 134; and a locking pin within a lot of the secondrotor element 136 configured to engage the latch 140 and preventseparation of the first rotor element 134 from the second rotor element136 in the engaged configuration of the concentric rotor assembly 102.Thus, a user may install and remove the concentric rotor assembly 102around a sprocket of a bicycle without tools and within a short periodof time and, while in the engaged configuration, the concentric rotorassembly 102 remains rigidly engaged around the bicycle sprocketsufficient to transfer torque from the drive subassembly to the sprocketof the bicycle.

The concentric rotor assembly 102 can include a latch 140 inset into afirst end of the first rotor element 134 and a latching pin 146traversing a slot in a second end of the second rotor element 136. Thus,when a user brings the first end of the first rotor element 134 and thesecond end of the second rotor element 136 together and slots the latch140 of the first rotor element 134 into the slot in the second rotorelement 136, the latch 140 latches around the latching pin 146, therebypreventing disengagement of the first rotor element 134 from the secondrotor element 136. Additionally, the concentric rotor assembly 102 caninclude a latch 140 configured to release a latching pin 146 upontranslation of a sliding member 148 mechanically coupled to the latch140 and configured to enclose the latch 140 inset in the rotor element.

In one implementation, the concentric rotor assembly 102 can include alatch 140 that further includes a spring-loaded linear cam 142configured to engage with a hooked follower 144, as shown in FIG. 9 .FIG. 9 shows the latch 140 in the locked position despite showing thefirst rotor element 134 and the second rotor element 136 as separatedfrom each other for clarity. Upon engagement of the rotor elements, thehooked follower 144 catches the latching pin 146 on the opposite rotorelement and rotates about a follower pin 145 until the linear cam 142can translate into a slot left by the rotation of the hooked follower144, thereby preventing back-rotation of the hooked follower 144 and, asa result, prevents disengagement of the latching pin 146 from the hookedfollower 144. The latch 140 can also include sliding member 148 (notshown for clarity in FIG. 9 ) that is mechanically coupled to the linearcam 142 to enable the hooked follower 144 to back rotate such that, uponapplication of a force separating the first rotor element 134 from thesecond motor 162, the latching pin 146 can be removed from the hook ofthe hooked follower 144 as the hooked follower 144 back-rotates.

In another implementation, the concentric rotor assembly 102 isconfigured to cooperate within the chassis assembly 104 in order to hidethe latch 140 within the chassis assembly 104, thereby preventing accessto the latch 140 and effectively locking the concentric rotor assembly102 around the sprocket of the bicycle for the purpose of theftprevention. More specifically, in this implementation, the chassisassembly 104 can include a solenoid, or another electromechanical latchwithin the chassis assembly 104, configured to engage with acorresponding slot, an indentation, or the outer drive surface 132 ofthe concentric rotor 130 such that, while the solenoid or latch isengaged, the concentric rotor is locked in place and the latch 140 isconcealed by the chassis assembly 104 (i.e., the outboard frame 114).Additionally, the latch or solenoid can be actuated by a physical key orvia wireless communication with an application executing a mobilecomputation device of the cyclist in order to engage and remove thelatch or solenoid from the slot of the concentric rotor 130, therebyenabling the concentric rotor 130 to freely rotate again. Furthermore,the bicycle propulsion system 100 can: store a predefined position ofthe concentric rotor for which the latch 140 (and sliding member 148) isblocked against the interior surface of the outboard frame 14; and, inresponse to receiving a command to lock bicycle propulsion system 100 tothe bicycle, the bicycle propulsion system can actuate the motor 162 tomove the concentric rotor assembly 102 into the predefined position andengage an electromechanical pin preventing rotation of the concentricrotor 102. Therefore, the bicycle propulsion system 100 can be locked tothe frame of the bicycle remotely without physical intervention by auser.

In yet another implementation, the bicycle propulsion system 100 caninclude other locking mechanisms such as integrated U-locks, cablelocks, or folding locks configured to secure the concentric rotorassembly 102 and/or the chassis assembly 104 to the frame or wheel ofthe bicycle. Additionally, the bicycle propulsion system 100 can includea GPS chip and an inertial measurement unit and can, while the bicycleis not in use (or upon activation of this security feature via mobilecomputational device of a user): detect movement of the bicycle and/orthe bicycle propulsion system 100; and transmit the GPS location of thebicycle propulsion system to a mobile computational device of the user.Thus, the concentric rotor assembly 102 can define security featuresconfigured to prevent removal of the concentric rotor 130 from thesprocket and/or removal of the chassis assembly 104 from the bicycle.

However, the concentric rotor assembly 102 can include any type of latch140 capable of securing the first rotor element 134 to the second rotorelement 136 when engaged with the sprocket of the bicycle and under loadby the drive subassembly.

3.5 Sprocket Brackets

Generally, as shown in FIG. 11 , the concentric rotor assembly 102 caninclude a set of sprocket brackets 150 configured to engage with teethof a bicycle sprocket such that torque applied to the concentric rotor130 is transferred to the sprocket of the bicycle. More specifically,the concentric rotor assembly 102 can further include a set of sprocketbrackets, each sprocket bracket defining: a set of outboard retainingteeth 154 configured to engage the outer surface of the sprocket of thebicycle; a set of inboard retaining teeth 155 offset from the outboardretaining teeth 154 by greater than the thickness of the sprocket of thebicycle and configured to engage the inner surface of the sprocket ofthe bicycle; and a set of engagement features 156 configured to engagewith pitches of the sprocket of the bicycle arranged between the set ofoutboard retaining teeth 154 and the set of inboard retaining teeth 155.Thus, the concentric rotor assembly 102 can engage with a sprocket of abicycle via the set of sprocket brackets 150.

The sprocket bracket can define a set of engagement features 156 thatare configured to sit within the pitches (i.e. between the teeth orspurs) of the bicycle sprocket when the sprocket bracket is engaged withthe sprocket of the bicycle. Therefore, the sprocket bracket can defineengagement features 156 that include a series of half-cylindrical spursmimicking one side of the rivets of a bicycle chain. In oneimplementation, the sprocket bracket can define engagement features 156that include a series of half-cylindrical spurs that are characterizedby a diameter less than the diameter of bicycle chain rivets configuredto engage the bicycle sprocket. By including slightly smaller diameterengagement features 156 than the rivets of a bicycle chain matched tothe bicycle sprocket, the sprocket bracket can more easily be installedonto the bicycle sprocket.

Additionally, the sprocket bracket can define a set of inboard retainingteeth 155 and outboard retaining teeth 154 on either side of theengagement features 156 in order to prevent lateral disengagement of thesprocket bracket from the sprocket of the bicycle (e.g., due tonon-axial torque applied to the concentric rotor assembly 102).Therefore, the sprocket bracket can include inboard retaining teeth 155and outboard retaining teeth 154 characterized by a thickness less thanthe intra-sprocket spacing of the cogset of the bicycle. Furthermore,the sprocket bracket can include inboard retaining teeth 155 andoutboard retaining teeth 154 that alternate on either side of theengagement features 156 in order facilitate engagement of the sprocketbracket with the sprocket of the bicycle by a user of the bicyclepropulsion system 100, as shown in FIG. 11 .

The concentric rotor assembly 102 can include a set of sprocket brackets150 with engagement features 156, inboard retaining teeth 155, andoutboard retaining teeth 154, configured to engage with a sprocket of aparticular size (i.e. number of teeth), with a sprocket configured for aparticular chain standard (e.g., half-inch pitched chain, eighth-inchchain, three-sixteenths-inch chain, 5.3-millimeter chain, 5.5-millimeterchains, six-millimeter chain, 6.5-millimeter chain, and/orseven-millimeter chain), and with a sprocket characterized by aparticular sprocket spacing. Thus, the sprocket bracket can defineengagement features 156, inboard retaining teeth 155, and outboardretaining teeth 154, characterized by dimensions corresponding to thesprocket of the bicycle with which the sprocket bracket is configured toengage.

In one implementation, each sprocket bracket in the set of sprocketbrackets 150 defines an engagement are characterized by a radius equalto or greater than the pitch radius of the sprocket of the bicycle withwhich the sprocket bracket is configured to engage. Thus, the curvatureof each sprocket bracket in the set of sprocket brackets 150approximately matches the curvature of the bicycle sprocket with whichthe sprocket bracket is configured to engage.

In another implementation, the concentric rotor assembly 102 can alsoinclude a set of sprocket brackets 150 that define a total arc lengththat is greater than 25% of the pitch circumference of the bicyclesprocket. Thus, in implementations of the concentric rotor assembly 102that include a first sprocket bracket 151 and a second sprocket bracket152, the first sprocket bracket 151 and the second sprocket bracket 152can be configured to engage with greater than twenty five percent ofteeth of the first bicycle sprocket in the engaged configuration of theconcentric rotor assembly 102. For example, the concentric rotorassembly 102 can include a first sprocket bracket 151 attached to afirst rotor element 134 and a second sprocket bracket 152 attached to asecond rotor element 136 configured to engage a sprocket defining 28teeth. In this example, the first sprocket bracket 151 and the secondsprocket bracket 152 together define an arc length and engagementfeatures 156 configured to engage with at least seven teeth of thesprocket.

In yet another implementation, the concentric rotor assembly 102 caninclude a set of sprocket brackets 150 that define a total arc lengthless than sixty percent of the pitch circumference of the bicyclesprocket. In this implementation, the set of sprocket brackets 150 canengage with less than 60% of the teeth of the bicycle sprocket. Forexample, the concentric rotor assembly 102 can include a first sprocketbracket 151 attached to a first rotor element 134 and a second sprocketbracket 152 attached to a second rotor element 136 configured to engagea sprocket defining 28 teeth. In this example, the first sprocketbracket 151 and the second sprocket bracket 152 together define an arclength and engagement features 156 configured to engage with sixteen orfewer teeth of the sprocket.

Generally, each sprocket bracket in the set of sprocket brackets 150attaches to a corresponding rotor element via a set of sprocket strutsconfigured to secure to a face of the concentric rotor 130, as shown inFIG. 5 . In one implementation, the set of sprocket struts define a setof threaded bores aligned with threaded bores inset into a face of theconcentric rotor 130, as shown in FIG. 11 . Thus, the set of sprocketbrackets 150 are replaceable and/or exchangeable by a user of thebicycle propulsion system 100.

In one implementation, the concentric rotor assembly 102 includes a setof sprocket brackets 150 configured to engage with an innermost bicyclesprocket in a bicycle cogset (e.g., the largest-diameter sprocket in thecogset). More specifically, in implementations of the bicycle propulsionsystem 100 including a first sprocket bracket 151 and a second sprocketbracket 152: the first sprocket bracket 151 is further configured toengage with an innermost bicycle sprocket in a bicycle cogset; thesecond sprocket bracket 152 is further configured to engage theinnermost bicycle sprocket; and the concentric rotor assembly 102 isfurther configured to transiently engage around the innermost bicyclesprocket of the bicycle via the first sprocket bracket 151 and thesecond sprocket bracket 152 in the engaged configuration of theconcentric rotor assembly 102; the retention subassembly is furtherconfigured to translationally constrain the concentric rotor assembly102 relative to the chassis assembly 104 while the concentric rotorassembly 102 is engaged around the innermost bicycle sprocket and thechassis assembly 104 is secured to the bicycle frame element; and themotor 162 is further configured to rotate the concentric rotor assembly102 about the center axis of the circular outer drive surface 132 viathe drive subassembly, the motor 162 causing rotation of the innermostbicycle sprocket while the concentric rotor assembly 102 is engagedaround the second bicycle sprocket. Thus, the concentric rotor assembly102 can include a set of sprocket brackets 150 configured to attach tothe inboard side of the concentric rotor 130 to avoid interference withother sprockets of the bicycle and defining a curve back outward suchthat the engagement features 156 are located between planes defined bythe inboard and outboard faces of the concentric rotor 130, as shown inFIG. 10 . In this implementation, the set of sprocket brackets 150 candefine filleted edges to reduce force concentration in each sprocketbracket.

The set of sprocket brackets 150 can be manufactured from anyhardwearing and lightweight material capable of transferring torque fromthe concentric rotor 130 to the sprocket of the bicycle, such asaluminum or steel. The set of sprocket brackets 150 can be manufacturedvia stamping milling, additive manufacturing, or any other manufacturingtechniques.

3.5.1 Sprocket Bracket Kit

In one implementation, the bicycle propulsion system 100 includesmultiple sets of sprocket brackets 150, each set configured to engagewith a different type of bicycle sprocket (e.g., for sprockets defininga different number of teeth or in compliance with a different standard).More specifically, in implementations of the bicycle propulsion system100 including a first sprocket bracket 151 and a second sprocket bracket152 in a first set of sprocket brackets 150: the first sprocket bracket151 is further configured to engage the first bicycle sprocket, thefirst bicycle sprocket characterized by a first number of teeth; thesecond sprocket bracket 152 is further configured to engage the firstbicycle sprocket, the first bicycle sprocket characterized by the firstnumber of teeth. The bicycle propulsion system 100 can further include:a third sprocket bracket configured to attach to the first rotor element134 in replacement of the first sprocket bracket 151 and configured toengage with a second bicycle sprocket, the second bicycle sprocketcharacterized by a second number of teeth different from the firstnumber of teeth; and a fourth sprocket bracket configured to attach tothe second rotor element 136 in replacement of the second sprocketbracket 152; and configured to engage the second bicycle sprocket thesecond bicycle sprocket characterized by the second number of teeth. Inthis implementation of the bicycle propulsion system 100: the concentricrotor assembly 102 is further configured to transiently engage aroundthe second bicycle sprocket in the engaged configuration of theconcentric rotor assembly 102 via the third sprocket bracket and thefourth sprocket bracket; the retention subassembly is further configuredto translationally constrain the concentric rotor assembly 102 relativeto the chassis assembly 104 while the concentric rotor assembly 102 isengaged around the second bicycle sprocket and the chassis assembly 104is secured to the bicycle frame element; and the motor 162 is furtherconfigured to rotate the concentric rotor assembly 102 about the centeraxis of the circular outer drive surface 132 via the drive subassembly,the motor 162 causing rotation of the second bicycle sprocket while theconcentric rotor assembly 102 is engaged around the second bicyclesprocket. Thus, the bicycle propulsion system 100 can include a kit ofsprocket brackets 150 including multiple sets of sprocket brackets 150,where each set is configured to engage with a particular type of cogset.The bicycle propulsion system 100 can therefore engage with a number ofdifferent types of cogsets defining varying numbers of teeth, chainstandards, or sprocket spacing by exchanging one set of sprocketbrackets 150 for another set of sprocket brackets 150.

4. Chassis Assembly

Generally, as shown in FIGS. 3, 4, 5, 6, and 7 , the bicycle propulsionsystem 100 includes a chassis assembly 104 that: houses the retentionsubassembly that translationally constrains the concentric rotorassembly 102 relative to the chassis assembly 104; houses the drivesubassembly that is configured to transfer power from the motor 162 tothe concentric rotor assembly 102; houses the electronics subsystem 180that controls the motor 162 and executes pedal assist and safetyprocesses; and secures the bicycle propulsion system 100 to the frame ofthe bicycle in order to prevent rotation of the system relative to theframe of the bicycle while the concentric rotor assembly 102 is in theengaged configuration. More specifically, the bicycle propulsion system100 includes a chassis assembly 104: configured to transiently secure toa stay of the bicycle; comprising a retention subassembly configured totranslationally constrain the concentric rotor assembly 102 relative tothe chassis assembly 104; comprising a drive subassembly configured toengage the circular outer drive surface 132 of the concentric rotorassembly 102; and a motor 162 configured to rotate the concentric rotorassembly 102 about a center axis of the circular outer drive surface 132via the drive subassembly. Additionally, in implementations where thebicycle propulsion system 100 secures to another frame element of thebicycle, the bicycle propulsion system 100 includes a chassis assembly104: configured to transiently secure to a bicycle frame element;comprising a retention subassembly configured to translationallyconstrain the concentric rotor assembly 102 relative to the chassisassembly 104 while the concentric rotor assembly 102 is engaged aroundthe first bicycle sprocket and the chassis assembly 104 is secured tothe bicycle frame element; comprising a drive subassembly configured toengage the concentric rotor assembly 102 via the circular outer drivesurface 132; and comprising a motor 162 configured to rotate theconcentric rotor assembly 102 about a center axis of the circular outerdrive surface 132 via the drive subassembly, the motor 162 causingrotation of the first bicycle sprocket while the concentric rotorassembly 102 is engaged around the first bicycle sprocket. Thus, thechassis assembly 104 houses and locates the motor 162, the drivesubassembly, and the retention subassembly such that the motor 162transfers torque to the concentric rotor assembly 102 via the drive belt164. The concentric rotor assembly 102 then transfers this torque to thesprocket via the set of sprocket brackets 150, thereby assisting thecyclist in applying torque to the sprocket of the bicycle.

The chassis assembly 104 includes a chassis that houses the retentionsubassembly, the drive subassembly, the motor 162, and the electronicssubsystem 180. The chassis assembly 104 can include a chassis configuredto house the abovementioned subassemblies and subsystems within a formfactor that fits within the chain stay and/or seat stay of mostbicycles.

In one implementation, as shown in FIGS. 3, 4, 5, 6, and 7 , the chassisincludes: an outboard frame 114; an outboard frame 114 parallel to theinboard frame 116; an electronics housing; and a motor cowling 113. Inthis implementation, the outboard frame 114 and the inboard frame 116are separated by a set of standoffs 118 fastened to the outboard frame114 and the inboard frame 116 via a set of threaded bores in theoutboard frame 114 and the inboard frame 116. Thus, the outboard frame114 and the inboard frame 116 contain the retention subassembly and thedrive subassembly between them. In this implementation, the electronicssubsystem 180 and motor 162 are attached outboard of the outboard frame114 and are housed within the electronics housing and motor cowling 113respectively. Thus, the chassis assembly 104 can define distinct regionsfor the mechanical and electronic components of the bicycle propulsionsystem 100.

The chassis assembly 104 can include an outboard frame 114 and aninboard frame 116 stamped from aluminum, steel or any other rigidmaterial in order to support the retention subassembly and the drivesubassembly. The chassis assembly 104 can also include an outboard frame114 and an inboard frame 116 that define attachment points for the axlesof rollers and gears (from the retention subassembly and the drivesubassembly) and the motor 162 axle, thereby locating each of thesecomponents relative to each other. The chassis assembly 104 can alsoinclude an outboard frame 114 that further defines attachment points forthe motor 162, the electronics subsystem 180, the electronics housingand the motor cowling 113. In one implementation, the chassis assembly104 can include an outboard frame 114 that includes an attachment pointfor a sensor arm 171. In another implementation, the chassis assembly104 can include an outboard frame 114 defining a derailleur stop 115,configured to extend into the path of a derailleur of the bicycle, shownin FIGS. 3, 4, and 5 , in order to prevent the derailleur of the bicyclefrom shifting the bicycle chain into the sprocket with which theconcentric rotor 130 is engaged, thereby preventing physicalinterference between the derailleur of the bicycle and/or the chain ofthe bicycle with the bicycle propulsion system 100. Thus, the chassisassembly 104 includes comprises a derailleur stop 115 configured toprevent a derailleur of the bicycle from shifting into the first bicyclesprocket.

The chassis assembly 104 can include an electronics housing manufacturedfrom a hard plastic or other rigid, non-conductive material in order toprevent dirt and/or water ingress to the electronics subsystem 180housed by the electronics housing, while also enabling wirelesscommunication between the electronics subsystem 180 and a personalcomputing device of a user. The chassis assembly 104 can include anelectronics housing manufactured via molding (e.g., injection molding)or additive manufacturing processes.

The chassis assembly 104 can also include a motor cowling 113 configuredto surround the motor 162 and prevent physical damage to the motor 162upon incidental impact. The motor 162 itself can include an additionalwaterproof housing separate from the motor cowling 113. In oneimplementation, the chassis assembly 104 includes a single plasticmember that functions as both the electronics housing and the motorcowling 113.

The chassis assembly 104 also includes an attachment mechanismconfigured to transiently secure the chassis assembly 104 to a frameelement of the bicycle in order to prevent rotation of the chassisassembly 104 about the concentric rotor assembly 102, upon applicationof torque to the concentric rotor assembly 102 by the chassis assembly104. In one implementation, the chassis assembly 104 includes anattachment mechanism configured to attach the chassis assembly 104 tothe drive-side chain stay of the bicycle. In this implementation, themotor 162 and motor cowling 113 can be positioned below the attachmentmechanism such that, while the bicycle propulsion system 100 is engagedwith the bicycle, the motor 162 and motor cowling 113 can extendoutboard from the outboard frame 114 beneath the drive side chain stayof the bicycle. In this implementation, the chassis assembly 104 caninclude a flexible rubber or fabric strap configured to wrap around thechain stay of the bicycle and connect to the outboard face of thechassis assembly 104. However, the chassis assembly 104 can includeother types of attachment mechanisms such as a clamp- or latch-basedattachment mechanism.

4.1 Retention Subassembly

Generally, as shown in FIG. 6 , the chassis assembly 104 includes aretention subassembly that further includes a set of inner retainingrollers 122 and a set of outer retaining rollers 124 configured tolocate the concentric rotor assembly 102 within the chassis assembly 104such that the drive belt 164 engages the outer drive surface 132 of theconcentric rotor assembly 102 while also enabling the concentric rotor130 to rotate about its center axis (e.g., as a hub-less wheel) whentorque is applied to the concentric rotor via the drive belt 164. Morespecifically, the chassis assembly 104 includes a retention subassemblyfurther including a set of retaining rollers configured totranslationally constrain the concentric rotor 130 subsystem as ahub-less wheel via contact with the inner retention surface 133 and thecircular outer drive surface 132. Additionally, the chassis assembly 104can include a retention subassembly that does not interfere with theteeth on the outer drive surface 132 of the concentric rotor assembly102, thereby reducing wear on and excess noise produced by the retentionsubassembly during operation of the bicycle propulsion system 100.Furthermore, the chassis assembly 104 can include a retentionsubassembly that enables removal of the concentric rotor assembly 102from the chassis assembly 104 such that a user may perform maintenanceon the mechanical components of the bicycle propulsion system 100.

The retention subassembly includes a set of inner retention rollersconfigured to ride along the inner retention surface 133 of theconcentric rotor assembly 102 without interfering with the set ofsprocket brackets 150 arranged about the inner retention surface 133 ofthe concentric rotor assembly 102. In one implementation, the retentionsubassembly includes two inner retention rollers to constrain (incombination with the set of outer retention rollers) the concentricrotor assembly 102 in two dimensions coplanar with the rotational planeof the concentric rotor assembly 102. In another implementation, theretention subassembly includes inner retention rollers defining aslotted outer surface and defining a chamfer on either side of theslotted surface such that the inner retention rollers fit across thecorresponding inner retention surface 133 of the concentric rotorassembly 102, thereby laterally constraining the concentric rotorassembly 102 within the slotted surfaces of the retention rollers. Inthis implementation, the retention subassembly can include a set ofretention rollers defining asymmetrical slots such that the inboard sideof the retention rollers in the set of retention rollers can clear thesprocket brackets 150 attached on the inboard side of the concentricrotor assembly 102.

The retention subassembly includes a set of outer retention rollersconfigured to ride along a chamfered edge of the outer drive surface 132of the concentric rotor assembly 102. Thus, the retention subassemblycontains the concentric rotor assembly 102 between the set of outerretention rollers and the set of inner retention rollers. In oneimplementation, the retention subassembly includes a set of outerretention rollers including two outer retention rollers. In anotherimplementation, the retention subassembly can include a set of outerretention rollers can define a slotted outer surface such that the teethof the outer drive surface 132 do not come into contact with the outerretention rollers and instead the outer retention rollers contact thechamfered surface of the concentric rotor assembly 102.

In one implementation, the retention subassembly includes rollersmanufactured from polyoxymethylene, molybdenum-disulfide-filled nylon,or any other hardwearing plastic.

4.2 Drive Subassembly

Generally, as shown in FIG. 6 , the chassis assembly 104 includes adrive subassembly, in order to transfer torque and power from the motor162 to the concentric rotor assembly 102. More specifically, the chassisassembly 104 can include a drive subassembly that further includes: adrive gear 166 coupled to the motor 162; a drive belt 164 configured toengage the drive gear 166 and the circular outer drive surface 132 ofthe concentric rotor assembly 102; and a set of drive belt rollers 168configured to maintain engagement of the drive belt 164 with the drivegear 166 and with the outer drive surface 132 of the concentric rotorassembly 102. Thus, the drive subassembly, by including the drive belt164 as the primary wear component of the bicycle propulsion system, canoperate with no grease, thereby reducing maintenance overhead, whileproducing less noise when compared to a chain or meshed geartransmission system. Additionally, the drive belt 164 can be easilyremoved from the drive gear 166 and drive belt rollers 168 and replacedfurther improving the serviceability of the bicycle propulsion system100.

The drive subassembly can include a drive gear 166 that shares an axlewith the motor 162 and functions to transfer power to the drive belt164. The drive belt 164 is then directed within the confines of theinboard frame 116 and the outboard frame 114, via the set of drive beltrollers 168, to conform with an arc of the outer drive surface 132 ofthe concentric rotor assembly 102, while the concentric rotor assembly102 is engaged with the chassis assembly 104. In one implementation afirst pair of drive belt rollers 168 located proximal to the drive gear166 maintain tension in the drive belt 164 around the drive gear 166while a third drive belt roller 168 extends the drive belt 164 toward anupper side of the chassis assembly 104 such that the drive belt 164meshes with the outer drive surface 132 of the concentric rotor assembly102 over a large arc, thereby distributing torque transfer across alonger length of the drive belt 164 in order to further reducemaintenance frequency of the bicycle propulsion system. In anotherimplementation, the drive subassembly can include a set of drive rollers168 defining a smooth outer surface and configured to engage the smoothside of the drive belt 164 in order to direct the drive belt 164 aroundthe drive gear 166 and around the outer drive surface 132 of theconcentric rotor assembly 102.

The drive subassembly can include a geared jockey (or idler) pulleyconfigured to redirect and tension a section of the drive belt 164between the pair of drive rollers 168 proximal to the drive gear 166 andthe drive roller located on the upper end of the chassis assembly 104.In implementations where the chassis assembly 104 defines a differentform factor than the form factor shown in FIGS. 3, 4, 5, 6, and 7 , thedrive subassembly can include different and/or additional drive rollers168 and/or jockey pulleys 169 in order to position the drive belt 164around the drive gear 166 and around a portion of the outer drivesurface 132 of the concentric rotor assembly 102.

In one implementation, the drive belt 164 includes a timing belt.Alternatively, the drive subassembly can include a friction belt. Inthis implementation, the drive gear 166 is replaced with a drive wheel,and the drive rollers 168 and jockey wheel are configured to increasethe tension in the friction belt when compared to the timing belt.

In another implementation, the drive subassembly can include a planetarygearbox arranged between the motor and the drive gear 166 and configuredto transfer torque between the drive gear 166 and the motor 162, therebyreducing backlash between the drive gear 166 and the motor 162. In thisimplementation, the planetary gearbox can be configured with the drivegear 166 as the sun gear in the planetary gearbox. Alternatively, theplanetary gearbox can be configured with the drive gear as the ring gearin the planetary gearbox.

In yet another implementation, the drive subassembly can include agearbox (e.g., a planetary gearbox) in replacement of thedrive-belt-based system described above. In this implementation, thedrive subassembly can include a gearbox arranged, within the chassisassembly 104, between the drive gear 166 and the outer drive surface132, when the bicycle propulsion system 100 is in the engagedconfiguration. In one example, the drive subassembly can include aplanetary gearbox (e.g., a single stage planetary gearbox), where thedrive gear 166 is configured as a sun gear in the planetary gearbox andthe carrier of the planetary gearbox is configured to transfer torque tothe outer drive surface 132 (e.g., via a toothed concentric surface). Inanother example, the drive subassembly can include a planetary gearbox,where the drive gear 166 is configured as a sun gear in the planetarygearbox and the ring gear of the planetary gearbox is configured totransfer torque to the outer drive surface 132 of the concentric rotorassembly 102.

However, the drive subassembly can include additional componentsconfigured to transfer torque between the motor 162 and the concentricrotor assembly 102 via the outer drive surface 132.

4.3 Motor

Generally, as shown in FIGS. 3, 4, and 7 , the chassis assembly 104includes a motor 162 configured to transfer torque to the drivesubassembly via the drive gear 166, which then transfers torque to theconcentric rotor assembly 102, causing rotation of the concentric rotorassembly 102 and, therefore, the sprocket to which the concentric rotorassembly 102 is engaged. In one implementation, the motor 162 includes acompact electric motor 162, such as a radial flux or axial flux motor162.

The motor 162 can be coupled to the outboard frame 114 of the chassisassembly 104, thereby preventing interference between the motor 162 andthe wheel of the bicycle. The motor 162 also includes an output shaftextending through the outboard frame 114 into the internal volume of thechassis assembly 104. This output shaft is coupled to the drive gear 166of the drive subassembly and transfers power to the drive belt 164.

In one example, the motor 162 is characterized by a peak power output ofgreater than 1000 watts and characterized by a sustained power output of350 watts in order to sufficiently augment the power of the cyclist overa sustained period of time. Additionally or alternatively, the chassisassembly 104 can include a motor 162 that is electronically limited(e.g., to an output of 350 watts) in order to comply with regionalgovernment regulations for motorized vehicles.

In one implementation, the chassis assembly 104 includes a clutchinterposed between and configured to selectively engage the output shaftand the drive gear 166 of the drive subassembly. In this implementation,the bicycle propulsion system 100 can engage the clutch upon activationof the motor 162 and can disengage the clutch upon deactivation of themotor 162, or while coasting, in order to reduce friction on the drivetrain in these circumstances due to internal resistance of the motor 162to free rotation of the output shaft. The cutch can also be configuredto disengage the output shaft and the drive gear 166 by default, therebylimiting motor drag on the rear wheel when the bicycle propulsion system100 is off or when the battery assembly 106 is discharged.

4.4 Sensor Subassembly

Generally, as shown in FIGS. 3, 4, 12A and 12B, the chassis assembly 104can include a sensor subassembly 170 configured to detect power appliedto the bicycle by the cyclist during operation of the bicycle propulsionsystem 100, thereby enabling the electronics subsystem 180 to executeclosed-loop control of the motor 162 in order to assist the cyclist inpropelling the bicycle based on the current effort of the cyclist. Inone implementation, the sensor subassembly 170 includes a sensor arm 171attached to a chain roller 176 configured to measure tension in thechain of the bicycle. In another implementation, the sensor subassembly170 is integrated into the motor 162 housing and configured to measurethe pressure of the motor 162 housing against a chain stay of thebicycle.

In addition to the implementations described below, the sensorsubassembly 170 can estimate the power input to the bicycle by thecyclist in any other way (such as by utilizing a separate powercommunicating with the bicycle propulsion system 100).

4.4.1 Sensor Arm

In one implementation shown in FIGS. 12A and 12B, the sensor subassembly170 can include a sensor arm 171 configured to: extend from the chassisassembly 104 to the chain of the bicycle; include a chain roller 176configured to engaged with the chain of the bicycle; and configured todeflect based on the tension in the chain of the bicycle. Morespecifically, the sensor subassembly 170 includes a sensor arm 171configured to engage with a bicycle chain via a chain roller 176 biasedagainst the chain of the bicycle while the concentric rotor assembly 102is engaged around the first bicycle sprocket and the chassis assembly104 is secured to the bicycle frame element; and an electronicssubsystem 180 configured to detect deflection of the sensor arm 171caused by tension in the bicycle chain and activate the motor 162 torotate the concentric rotor 130 based on the deflection of the sensorarm 171. Thus, the sensor subassembly 170 can detect the tension in thechain of the bicycle such that the electronics subsystem 180 canestimate an applied power by the cyclist based on this detected tension,and execute closed-loop control of the motor 162 based on this estimatedpower.

In one implementation, the sensor subassembly 170 includes a sensor arm171 that is biased against the chain of the bicycle by a spring at oneend and engages with the chain with a chain roller 176 at the oppositeend. More specifically, the sensor subassembly 170 includes: a chainroller 176 coupled to the sensor arm 171 at a first end; and a biasingspring coupled to a second end of the sensor arm 171 and the chassisassembly 104 and configured to bias the chain roller 176 against thechain of the bicycle. Thus, the sensor assembly includes a sensor arm171 configured as a lever with a sensor arm 171 axle as a fulcrum with aspring attached at one end of the sensor arm 171 biasing the oppositeend toward the chain of the bicycle.

The sensor subassembly 170 further includes a chain roller 176 in orderto engage with the chain and ensure that deflection of the sensor arm171 is not due to the shape of the chain and is instead caused by thetension in the chain. Thus, the chain roller 176 can define a pitchedsurface configured engage the links of the chain to reduce periodicdeflection of the chain roller 176 as the chain roller 176 rolls alongthe chain. As shown in FIG. 13 , the chain roller 176 can define apitched surface and is constructed from: a set of pitched shells 185installed around the roller axle, the pitched shells defining a seriesof valleys 187 and peaks 189, where the distance between consecutivevalleys and consecutive peaks is equal to the pitch of the bicyclechain. Additionally, the chain roller 176 can include a rubber sleeve191 configured to be tensioned around the outside surface of theinstalled pitched shells 185.

As shown in FIG. 2 , the sensor subassembly 170 can include a chainroller 176 that is biased downward toward the chain such that the angleα is less than 180 degrees. Additionally, the sensor subassembly 170 caninclude a chain roller 176 that extends across the full length of thecogset of the bicycle to ensure contact with the chain irrespective ofthe current gear selection of the cyclist. Due to the changes in theangle of the chain of the bicycle dependent on the current gearselection, the sensor assembly can be configured to remain biasedagainst the chain for the full range of possible chain anglescorresponding to the full range of possible gear selections for atypical bicycle (e.g., an 8-speed, 9-speed, 10-speed, 11-speed, 12 speedand/or a 13-speed system).

In one implementation, shown in FIGS. 12A and 12B, the sensor assemblyincludes a sensor arm 171 further including a pivot 178 attached to anaxle of the chain roller 176, where the pivot 178 is configured to biasthe chain roller 176 against the chain of the bicycle and position theroller axle 177 perpendicular to the chain of the bicycle in a firstposition (shown in FIG. 12A); and configured to remove the chain roller176 from the chain of the bicycle in a second position (shown in FIG.12B). Thus, during installation of the bicycle propulsion system 100 bya user, the user may fold the chain roller 176 such that the roller axle177 is coplanar with the outboard frame 114 of the chassis assembly 104,thereby facilitating installation by preventing the chain roller 176from being caught on the chain while the bicycle propulsion system 100is moved into position at the chain stay of the bicycle.

In another implementation, the sensor assembly can include a sensor arm171 further including: a chain roller 176 coupled to the sensor arm 171at a first end; and a magnet 175 coupled to a second end. In thisimplementation, the electronics subsystem 180 (further described below)includes a Hall effect sensor proximal to the second end of the sensorarm 171 and is configured to detect deflection of the sensor arm 171 viathe Hall effect sensor based on displacement of the magnet 175. Thus, bythe inclusion of a magnet 175 at one end of the sensor arm 171, thebicycle propulsion system 100 can measure the deflection of sensor arm171 due to tension in the chain of the bicycle via one or more Halleffect sensors arranged within the electronics subsystem 180 proximal tothe second end of the sensor arm 171.

4.4.2 Pressure Sensor

In one implementation, the sensor assembly includes a pressure sensorintegrated into the top side of the motor cowling 113 or electronicshousing and configured to measure the pressure applied by the bicyclepropulsion system 100 on the chain stay of the bicycle. Due to thearrangement of the motor cowling 113 below the chain stay of the bicyclein this implementation, an increase in torque applied by the motor 162compared to torque applied by the cyclist increases the pressure exertedby the chassis assembly 104 on the chain stay. Therefore, by measuringthe pressure in this location, the bicycle propulsion system 100 cancorrelate this pressure with the power input to the bicycle by thecyclist and adjust the power of the motor 162 accordingly.

4.5 Electronics Subsystem

Generally, as shown in FIG. 7 , the chassis assembly 104 includes anelectronics subsystem 180 that can further include a controller, a6-axis inertial measurement unit (or a 3-axis accelerometer and a 3-axisgyroscope), and/or a set of Hall effect sensors. Thus, the electronicssubsystem 180 can regulate power from the battery assembly 106 to themotor 162 in order to selectively apply torque to the sprocket of thebicycle in response to riding conditions detectable by the inertialmeasurement unit and the set of Hall effect sensors in cooperation withthe sensor subassembly 170. Additionally, the electronics subsystem 180can measure the orientation of the chassis assembly 104 relative to theground and estimate the speed of the bicycle in order to identifywhether the bicycle propulsion system 100 is operating with its safeoperational envelope. Furthermore, the electronics subsystem 180 canwirelessly communicate with a mobile computation device—such assmartphone, tablet, or smartwatch worn or carried by the cyclist—inorder to report ride-related data such as the current battery charge,the current level of pedal assistance, and/or the current operatingpower of the motor 162.

Generally, the controller can include a processor configured to executeoperational envelope detection and pedal assistance algorithms of thebicycle propulsion system 100. Thus, the controller can access data fromthe various sensors included in the electronics subsystem 180 and fromthe controller and can wirelessly communicate (e.g., via an integratedwireless chip) with other I/O devices in order to execute variousprocesses further described below.

4.5.1 Operational Envelope Detection

In one implementation, the electronics subsystem 180 is configured todetect whether the bicycle propulsion system 100 is within itsoperational envelope in order to ensure that the bicycle propulsionsystem 100 only applies power to the sprocket of the bicycle while theconcentric rotor assembly 102 is engaged with the sprocket of thebicycle, while the chassis assembly is secured to a frame element of thebicycle, and while the bicycle itself is in a safely operable state(e.g., not exceeding a maximum speed or in an inoperable orientation).More specifically, the electronics subsystem 180 is configured to, inresponse to detecting the position of the chassis assembly 104 outsideof a predefined operational envelope, halting the motor 162. Thus, thebicycle propulsion system 100 can ensure that power is cut from themotor 162 in the case of a crash or dislodgement of the bicyclepropulsion system 100 from its nominal position relative to the bicycle.

In one implementation, the electronics subsystem 180 can store a set ofparameters indicating the operational envelope for the bicyclepropulsion system 100, such as a maximum and minimum lateral angle (i.e.inboard/outboard tilt), a maximum and minimum transverse angle (i.e.forward and backward tilt), a maximum and minimum speed, and the stateof engagement of the sensor subassembly 170. In this implementation, theelectronics subsystem 180 can measure the orientation of chassisassembly prior to and/or during operation of the bicycle propulsionsystem 100 and in response to detecting that the orientation of thechassis assembly 104 exceeds the maximum lateral angle and/or themaximum transverse angle and/or is less than the minimum lateral angleor the minimum transverse angle, the electronics subsystem 180 haltsand/or cuts power to the motor 162. In one example, the electronicssubsystem 180 can halt the motor 162 in response to detecting a lateralangle greater than 30 degrees from vertical. Likewise, the electronicssubsystem 180 can estimate the speed of the chassis assembly 104 byexecuting an inertial algorithm on data recorded via the inertialmeasurement unit and, in response to detecting a speed exceeding themaximum speed or a speed less than the minimum speed, the electronicssubsystem 180 can halt the motor 162.

Additionally, the electronics subsystem 180 can measure velocity of thechassis assembly in multiple dimensions and can store multiple maximumand minimum velocities, each corresponding to velocity measured in adifferent dimension. Thus, the electronics subsystem 180 can detectlateral movement (e.g., skidding) and halt the motor 162 to enable thecyclist to more easily regain traction between the rear wheel and theground.

In another implementation, the electronics subsystem 180 can detectwhether the sensor arm 171 is engaged with the chain by detectingwhether the sensor arm 171 is deflected by less than a thresholddeflection caused by a tensionless chain. For example, the electronicssubsystem 180 can include a predefined deflection corresponding to astate where the sensor arm 171 is not engaged with the chain and isfully biased (e.g., by the biasing spring) against a hard stopintegrated within the chassis assembly 104. Therefore, in response todetecting that the chain is disengaged with the chain roller 176 of thesensor arm 171 and the tension of the chain is no longer detected by theelectronics subsystem 180, the electronics subsystem 180 can halt themotor 162.

4.5.2 Adaptive Pedal Assistance

Generally, the electronics subsystem 180 can execute an adaptive pedalassistance algorithm based on the estimated power output by the cyclist(e.g., via measurement of chain tension by the sensor subassembly 170,via integration with a power meter, or via a pressure sensor detectingthe force exerted by the chassis assembly 104 on the chain stay of thebicycle), the current gear selection of the cyclist, the cadence of thecyclist, the estimated inclination of the bicycle, and/or the estimatedspeed of the bicycle in order to selectively apply additional power tothe sprocket of the bicycle without substantially altering the handlingof the bicycle or the operational experience of the bicycle whencompared to manual operation of the same bicycle. More specifically, theelectronics subsystem 180 is configured to estimate the power output bythe cyclist based on deflection of the sensor arm 171 caused by tensionin the bicycle chain and modify the output power of the motor 162 basedon this measured deflection; estimate the gear selection of the bicyclebased on step changes in the deflection of the sensor arm 171; estimatethe inclination of the bicycle relative to the ground plane based ondata from the inertial measurement unit; and estimate the speed of thebicycle based on an estimated cadence of the cyclist and the gearselection of the bicycle.

In one implementation, the electronics subsystem 180 can store apredefined lookup table (based on empirical data) or a predefinedfunction correlating deflection of the sensor arm 171 to the poweroutput by the cyclist. In this implementation, the electronics subsystem180 can receive (e.g., via an associated application running on asmartphone) the gear configuration (e.g., brand cassette and chainringselection) of the bicycle. The electronics subsystem 180 can then selecta function or lookup table corresponding to the gear configuration ofthe bicycle.

Alternatively, the electronics subsystem 180 can initiate a calibrationprocedure based on input from a mobile computation device (e.g., via anassociated application running on a smartphone) in order to associatethe power output by the cyclist with deflection of the chain. During thecalibration procedure, the electronics subsystem 180 can measure thedeflection of the chain of the bicycle as the cyclist is instructed toperform a series of hard and easy efforts. Based on these data, theelectronics subsystem 180 can then correlate the deflection of the chainof the bicycle with maximum and minimum efforts of the cyclist.

In another implementation, the electronics subsystem 180 can: store amodel, map, or lookup table that links predefined deflection ranges ofthe sensor arm to a particular sprocket selection in the rear cogset;measure deflection of the sensor arm 171; and predict the gear selectionof the bicycle based on this model and the measured deflection.Alternatively, the electronics subsystem 180 can execute a calibrationprocedure by: for a first sprocket in the cogset of the bicycle,prompting the cyclist to shift into the first sprocket and pedal (e.g.,at variable effort levels); recording deflection of the sensor arm 171for a first duration; and repeating this procedure for successivesprockets of the cogset of the bicycle.

In yet another implementation, the electronics subsystem 180 can:execute frequency analysis on the measured deflection of the sensor arm171 over time to estimate the cadence of the cyclist; and modify thepower output by the motor 162 based on the cadence of the cyclist. Forexample, in response to estimating a low cadence of the cyclist (e.g.,less than 70 rotations-per-minute), the electronics subsystem 180 canincrease the power output of the motor 162. Alternatively, in responseto estimating a high cadence of the cyclist (e.g., greater than 100rotations-per-minute), the electronics subsystem 180 can decrease thepower output of the motor 162. Thus, the electronics subsystem 180leverages the cyclic nature of the torque applied by the cyclist duringeach pedal stroke to estimate the cadence of the cyclist and can modifythe power output of the motor 162 based on this estimated cadence.

In another implementation, the electronics subsystem 180 can estimatethe inclination of the bicycle by calculating, via the inertialmeasurement unit, the transverse orientation of the chassis assembly104. Based on a known orientation of the chassis assembly 104 while thebicycle is on flat ground, the electronics subsystem 180 can calculatethe inclination of the bicycle and modify the power output of the motor162 based on this inclination.

In another implementation, the electronics subsystem 180 can implementdead reckoning techniques to estimate the speed of the speed of thebicycle based on inertial data output by the inertial measurement unit.Additionally or alternatively, the electronics subsystem 180 cancalculate the speed of the bicycle directly based on the estimatedcadence of the cyclist, the estimated gear selection of the bicycle, anda known wheel diameter of the bicycle. In yet another implementation,the electronics subsystem 180 can: measure a rotational speed of themotor 162 (e.g., via a rotational encoder, via Hall effect sensorsproximal to the motor, or via measurement of the counter-electromotiveforce of the motor 162); and estimate the speed of the bicycle based onthe measured rotational speed of the motor 162, the gear ratio betweenthe motor 162 and the wheel of the bicycle, and the known wheel diameterof the bicycle.

Upon calculating and/or estimating each of the above values, theelectronics subsystem 180 can input these values into a tuned functionin order to calculate an output power for the motor 162. The electronicsubsystem 180 then communicates this output power to the motor 162; anddraws power from the battery assembly 106 sufficient to operate themotor 162 at this output power. In one implementation, the electronicssubsystem 180 is configured to calculate an output power of zero upondetecting a speed of the bicycle greater than a threshold speed in orderto comply with regulations on electric bicycles.

Thus, the electronics subsystem 180 can be configured to: calculate acadence of the bicycle based on periodic deflection of the sensor arm171; calculate a speed of the bicycle via the six-axis inertialmeasurement unit; identify a current gear ratio of the bicycle based onthe speed of the bicycle and the cadence of the bicycle; and drive themotor 162 based on the current gear ratio of the bicycle.

4.5.3 Automatic Backpedaling Assistance

In one implementation, the electronics subsystem 180 can executeautomatic backpedaling assistance to enable the bicycle equipped withthe bicycle propulsion system 100 to mimic the pedaling dynamics of astandard bicycle. Because, the concentric rotor assembly 102, the drivesubassembly, and the motor 162 all impose additional resistance (e.g.,in the form of friction, additional rotational weight) onto the sprocketwhen the motor 162 is not powered, without automatic backpedalingassistance, the cyclist may be unable to backpedal the bicycle. Thus,upon detecting that the cyclist is no longer pedaling (e.g., based onthe chain tension estimated via the sensor arm 171), the electronicssubsystem 180 can cause the motor 162 to reverse direction at apredetermined speed, thereby enabling the user to pedal backward up to athreshold cadence corresponding to the predetermined backpedaling speed.

5. Battery Assembly

Generally, as shown in FIG. 1 , the bicycle propulsion system 100 caninclude a battery assembly 106 connected to the chassis assembly 104 bya power cable 182 (or integrated directly with the chassis assembly 104)in order to supply power to the electronics subsystem 180 and the motor162). In one implementation, the bicycle propulsion system 100 isconfigured to: fit within a standard bicycle bottle holder; supply powerto the motor 162; and supply power to the electronics subsystem 180. Inthis implementation, the battery assembly 106 also includes a powercable 182 electrically coupling the battery assembly 106 to theelectronics subsystem 180 and the motor 162. Thus, by including abattery assembly 106 that fits within a standard bicycle bottle holder,the bicycle propulsion system 100 can be more easily installed on anybicycle already including a standard bottle holder.

In one implementation, the bicycle propulsion system 100 includes abattery assembly 106 further including a set of modular battery packsconfigured to engage with each other and configured to fit within astandard bicycle bottle holder. This modular battery assembly 106enables the user to bring only the battery capacity needed for a plannedtrip and reduce the total weight of the bicycle propulsion system 100 inaccordance with the needed capacity. In one example, the batteryassembly 106 can include a set of cylindrical modular batteriesconfigured to connect at the top and bottom of the cylinder andconfigured to slide into a standard bicycle bottle holder. Additionally,in this example the battery assembly 106 can include a topmostcylindrical battery configured to engage the power cable 182 and abottommost cylindrical battery defining a flat bottom such that thebottommost cylindrical battery rests evenly at the bottom of a standardbicycle bottle holder. In another example, the battery assembly 106 caninclude an exterior battery shell (e.g., in the form of a hollowcylinder) and configured to support a set of modular batteries withinthe exterior battery shell. In this example, the exterior battery shellcan include an integrated electronic battery management unit connectedto each modular battery in the set of modular batteries in order tomodulate power drawn from each modular battery in the set of modularbatteries. The exterior battery shell can be configured to secure theset of modular batteries within the exterior battery shell via frictionor via a set of mechanical locks or latches. Each modular batter in theset of modular batteries can include a female surface and a male surfaceon the top and bottom of the modular battery respectively (or viceversa) in order to aid in engaging each modular battery with othermodular batteries in the set of modular batteries. Additionally, in thisexample, the topmost modular battery in the set of modular batteries aninclude a connector or adapter configured to electrically couple thebattery assembly 106 to the power cable 182.

In another implementation, the bicycle propulsion system 100 can includea battery assembly 106 integrated with the chassis assembly 104 orconfigured to attach to the chain stay, seat stay, seat tube, downtube,or top tube of the bicycle. In each implementation, the bicyclepropulsion system 100 can include a power cable 182 of an appropriatelength to connect the battery assembly 106 the chassis assembly 104.Alternatively, the bicycle propulsion system 100 can include a batteryassembly 106 that directly connects directly the chassis assembly 104without a power cable 182.

6. Throttle Assembly

In one variation shown in FIG. 1 , the bicycle propulsion system 100includes a throttle assembly 108. For example, the throttle assembly 108can include a set of buttons and can transmit button selections to thecontroller. The controller can then: adjust a relationship between chaintension (or cyclist output power) and torque or power output of themotor; or switch the bicycle propulsion system 100 on and off based onselections of these buttons. The throttle assembly 108 can additionallyor alternatively display system data received from the controller, suchas battery level, assistance level, and/or ride statistics.

7. Chainring-Mounted Variation

In one variation, the bicycle propulsion system 100 is configured toengage with one or more front sprockets (i.e. chainrings) of the bicycle(as opposed to the rear cogset) in order to convert bicycles withoutsufficient clearance in proximal to the rear triangle of the bicycle ormountain bikes with cogset sprockets above a threshold diameter to anelectrically assisted bicycle. In this variation, the bicycle propulsionsystem 100 can include a concentric rotor assembly 102 configured toengage with an innermost set of chainrings of the bicycle and a chassisassembly 104 configured to rest between the seat tube and the downtubeof the bicycle or configured to attach below the downtube of thebicycle. Alternatively, in this variation, the bicycle propulsion system100 can include a concentric rotor assembly 102 configured to engagewith the outermost chainring of the bicycle. This variation of thebicycle propulsion system 100 can include the same set of componentsdescribed above with respect to the rear cogset variation that insteaddefines a form factor configured to fit within the bottom bracket regionof the bicycle.

8. Disk-Brake-Mounted Variation

In another variation, the bicycle propulsion system 100 is configured tomount to and/or replace the rear disk brake rotor and the rear diskbrake caliper of a disk brake bicycle in order to vacate the innermostsprocket, thereby enabling use of the entire cogset of the bicycle. Morespecifically, in this variation, the bicycle propulsion system 100 caninclude: a concentric rotor assembly 102 configured to replace the reardisk brake rotor of the disk brake bicycle and including a brakingsurface; and a chassis assembly 104 configured to mount to the left siderear chain stay and/or the left side rear seat stay and including abraking caliper. Thus, in this variation, the bicycle propulsion system100 can drive the rear wheel of the bicycle via a concentric rotorassembly 102 configured to replace the disk brake rotor of a disk brakebicycle and can replace the functionality of the replaced disk brakerotor via the inclusion of a braking surface on the concentric rotorassembly 102. Additionally, in this variation, the concentric rotorassembly 102 can include a center axle that replaces the through-axle ofthe disk brake assembly and can, therefore, be driven via a direct powertransmission between the motor 162 and this through-axle. Alternatively,in this variation of the bicycle propulsion system 100, the concentricrotor assembly 102 can include an outer drive surface 132 and thebicycle propulsion system 100 can apply torque to this outer drivesurface 132 via the drive subassembly as described above.

The systems and methods described herein can be embodied and/orimplemented at least in part as a machine configured to receive acomputer-readable medium storing computer-readable instructions. Theinstructions can be executed by computer-executable componentsintegrated with the application, applet, host, server, network, website,communication service, communication interface,hardware/firmware/software elements of a user computer or mobile device,wristband, smartphone, or any suitable combination thereof. Othersystems and methods of the embodiment can be embodied and/or implementedat least in part as a machine configured to receive a computer-readablemedium storing computer-readable instructions. The instructions can beexecuted by computer-executable components integrated bycomputer-executable components integrated with apparatuses and networksof the type described above. The computer-readable medium can be storedon any suitable computer readable media such as RAMs, ROMs, flashmemory, EEPROMs, optical devices (CD or DVD), hard drives, floppydrives, or any suitable device. The computer-executable component can bea processor but any suitable dedicated hardware device can(alternatively or additionally) execute the instructions.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the embodiments of the invention without departing fromthe scope of this invention as defined in the following claims.

I claim:
 1. A bicycle propulsion system comprising: an annular rotorassembly: operable in an open configuration and a closed configuration;and comprising: a first rotor element; a second rotor elementcooperating with the first rotor element to form a circular outer drivesurface around a first bicycle sprocket in the closed configuration; afirst sprocket bracket extending inwardly from the first rotor elementand configured to engage the first bicycle sprocket in the closedconfiguration; and a second sprocket bracket extending inwardly from thesecond rotor element and configured to engage the first bicycle sprocketin the closed configuration; and a chassis assembly: configured totransiently couple to a frame element of a bicycle; comprising aretention subassembly configured to locate the annular rotor assembly,in the closed configuration, relative to the chassis assembly;comprising a motor; and comprising a drive subassembly configured totransfer torque output by the motor into the circular outer drivesurface, formed by the first rotor element and the second rotor elementin the closed configuration, to rotate the first bicycle sprocket viathe first sprocket bracket and the second sprocket bracket.
 2. Thebicycle propulsion system of claim 1: wherein a second rotor elementcooperates with the first rotor element to form the circular outer drivesurface comprising a continuous toothed gear around and concentric withthe first bicycle sprocket in the closed configuration; and wherein thedrive subassembly comprises a toothed gear: arranged on an output shaftof the motor; and configured to mesh with the continuous toothed gearformed by the first rotor element and the second rotor element in theclosed configuration.
 3. The bicycle propulsion system of claim 1:wherein the first sprocket bracket and the second sprocket bracket areconfigured to engage the first bicycle sprocket in the closedconfiguration, the first bicycle sprocket defining a first diameter andan outer sprocket face opposite a rear wheel of the bicycle wherein thefirst sprocket bracket defines a first outer face inset from an innersprocket face of a second bicycle sprocket, the second bicycle sprocketadjacent the first bicycle sprocket, opposite the bicycle wheel, anddefining a second diameter less than the first diameter; and wherein thesecond sprocket bracket defines a second outer face inset from the innersprocket face of the second bicycle sprocket.
 4. The bicycle propulsionsystem of claim 3, wherein the chassis assembly further comprises aderailleur stop configured to prevent a derailleur of the bicycle fromtransferring a chain from the second bicycle sprocket onto the firstbicycle sprocket.
 5. The bicycle propulsion system of claim 1: wherein,in the closed configuration, the first rotor element and the secondrotor element form the outer drive surface defining a continuous timingbelt pulley; wherein the chassis assembly defines a semicircular reliefconfigured to receive less than half of an arc length of the circularouter drive surface defined by the first rotor element and the secondrotor element in the closed configuration; and wherein the drivesubassembly comprises: a set of drive belt rollers adjacent thesemicircular relief; a drive pulley mounted to the motor; and a timingbelt configured to: mesh with the drive pulley; run on the set of drivebelt rollers; mesh with the outer drive surface; and transfer torqueoutput by the motor into the circular outer drive surface.
 6. Thebicycle propulsion system of claim 5: wherein the second rotor elementcooperates with the first rotor element to form a first running surfaceon a first side of the circular outer drive surface and a second runningsurface on a second side of the circular outer drive surface in theclosed configuration; and wherein the retention subassembly comprises aset of outer retaining rollers: adjacent the semicircular relief; andconfigured to ride on the first running surface and the second runningsurface of the annular rotor assembly to laterally and longitudinallyconstrain the annular rotor assembly, in the closed configuration,relative to the chassis assembly.
 7. The bicycle propulsion system ofclaim 6: wherein the second rotor element cooperates with the firstrotor element to form an inner retention surface inset the circularouter drive surface in the closed configuration; and wherein theretention subassembly further comprises a set of inner retainingrollers: adjacent the semicircular relief; configured to ride on theinner retention surface; and cooperating with the set of outer retainingrollers to constrain the annular rotor assembly, in the closedconfiguration, relative to the chassis assembly in three degrees oftranslation and two degrees of rotation.
 8. The bicycle propulsionsystem of claim 1, wherein the first sprocket bracket defines: a firstset of engagement features configured to insert between and to engageteeth of the first bicycle sprocket; a second set of engagementfeatures: configured to insert between and to engage teeth of the firstbicycle sprocket; and interdigitated between the first set of engagementfeatures; a first set of outboard retaining teeth arranged on left sidesof the first set of engagement features; and a second set of outboardretaining teeth: arranged on right sides of the second set of engagementfeatures; and configured to laterally constrain the first sprocketbracket on the first bicycle sprocket.
 9. The bicycle propulsion systemof claim 1: wherein the first sprocket bracket is transiently coupled toand extends inwardly from the first rotor element by a first length tomesh with the first bicycle sprocket characterized by a first bicyclesprocket diameter; wherein the second sprocket bracket is transientlycoupled to and extends inwardly from the second rotor element by thefirst length to mesh with the first bicycle sprocket; and furthercomprising: a third sprocket bracket: configured to couple to the firstrotor element in replacement of the first sprocket bracket; andextending inwardly from the first rotor element by a second lengthgreater than the first length to mesh with a second bicycle sprocketcharacterized by a second sprocket diameter less than the first bicyclesprocket diameter; and a fourth sprocket bracket: configured to coupleto the first rotor element in replacement of the first sprocket bracketand in conjunction with the third sprocket bracket; and extendinginwardly from the second rotor element by the second length to mesh withthe second bicycle sprocket.
 10. The bicycle propulsion system of claim1: wherein the first rotor element and the first sprocket bracket arephysically coextensive; and wherein the second rotor element and thesecond sprocket bracket are physically coextensive.
 11. The bicyclepropulsion system of claim 1: wherein the first rotor element: defines afirst end; defines a second end opposite the first end; and comprises alatching pin proximal the second end; wherein the second rotor element:defines a third end pivotably coupled to the first end of the firstrotor element; defines a fourth end opposite the third end; comprises alatch proximal the fourth end; and configured to engage the latching pinto retain the first rotor element and the second rotor element in theclosed configuration.
 12. The bicycle propulsion system of claim 11,wherein the first rotor element pivots on the second rotor element totransition the annular rotor assembly from the closed configuration tothe open configuration, the first sprocket bracket and the secondsprocket bracket decoupled from the first bicycle sprocket in the openconfiguration.
 13. The bicycle propulsion system of claim 1: wherein thefirst rotor element spans a first arc segment of a first arcuate length;and wherein the second rotor element; spans a second arc segment of asecond arcuate length; and cooperates with the first rotor element toform a contiguous annulus, concentric with first bicycle sprocket, inthe closed configuration.
 14. The bicycle propulsion system of claim 13:wherein the first sprocket bracket comprises a first mesh: configured toengage a first subset of teeth of the first bicycle sprocket in theclosed configuration; and spanning a third arc segment of a thirdarcuate length less than the first arcuate length; and wherein thesecond sprocket bracket comprises a second mesh: configured to engage asecond subset of teeth, distinct from the first subset of teeth, of thefirst bicycle sprocket in the closed configuration; and spanning afourth arc segment of a fourth arcuate length less than the secondarcuate length.
 15. The bicycle propulsion system of claim 13, whereinthe first sprocket bracket and the second sprocket bracket cooperate tomesh with between 25 percent and 60 percent of teeth of the firstbicycle sprocket in the closed configuration.
 16. The bicycle propulsionsystem of claim 1, wherein the chassis assembly further comprises: aroller sprung against and configured to ride on a bicycle chain of thebicycle; a sensor configured to output a signal representing a positionof the roller; and a controller configured to: interpret a tension inthe bicycle chain based on the position of the roller; and actuate themotor to rotate the annular rotor assembly based on the tension in thebicycle chain.
 17. The bicycle propulsion system of claim 16, whereinthe controller is configured to control torque output of the motorproportional to the tension in the bicycle chain.
 18. A bicyclepropulsion system comprising: a first rotor element; a second rotorelement cooperating with the first rotor element to form: a circularouter drive surface around a first bicycle sprocket in a closedconfiguration; and decoupled from the first bicycle sprocket in an openconfiguration; a first sprocket bracket inset from the first rotorelement, coupled to the first rotor element, and configured to engagethe first bicycle sprocket in the closed configuration; a secondsprocket bracket inset from the second rotor element, coupled to thesecond rotor element, and configured to engage the first bicyclesprocket in the closed configuration; a chassis configured totransiently couple to a frame element of a bicycle; a rotor retainerarranged on the chassis and configured to locate the first rotor elementand the second rotor element, in the closed configuration, relative tothe chassis; a motor mounted to the chassis; and a drive assembly:arranged on the chassis; and configured to transfer torque output by themotor into the circular outer drive surface, formed by the first rotorelement and the second rotor element in the closed configuration, torotate the first bicycle sprocket via the first sprocket bracket and thesecond sprocket bracket.
 19. A bicycle propulsion system comprising: afirst rotor element; a second rotor element cooperating with the firstrotor element to form an outer drive surface around a first bicyclesprocket in a closed configuration; and a first sprocket interface insetfrom the first rotor element and configured to transmit torque from thefirst rotor element into the first bicycle sprocket in the closedconfiguration; a second sprocket interface inset from the second rotorelement and configured to transmit torque from the second rotor elementinto the first bicycle sprocket in the closed configuration; a chassisconfigured to transiently couple to a bicycle frame; a rotor retainerarranged on the chassis and configured to locate the first rotor elementand the second rotor element, in the closed configuration, relative tothe chassis; a motor mounted to the chassis; and a drive assembly:arranged on the chassis; and configured to transfer torque output by themotor into the circular outer drive surface, formed by the first rotorelement and the second rotor element in the closed configuration, torotate the first bicycle sprocket.
 20. The bicycle propulsion system ofclaim 19, further comprising: a roller: arranged on the chassis; andsprung against and configured to ride on a bicycle chain of the bicycle;a sensor: arranged on the chassis; and configured to output a signalrepresenting a position of the roller; and a controller arranged on thechassis; and configured to: interpret a tension in the bicycle chainbased on the position of the roller; and actuate the motor to rotate theannular rotor assembly based on the tension in the bicycle chain.